Silicon semiconductor processing has evolved sophisticated operations for fabricating integrated circuits. As advancement in fabrication process technology continues, operating voltages of integrated circuits have decreased, but operating voltages of auxiliary devices remain the same. The auxiliary devices are devices used in conjunction with the integrated circuits, such as, printers, scanners, disk drives, tape drives, microphones, speakers, and cameras to provide some examples.
An integrated circuit may include an interconnected array of active and passive elements, such as, transistors, resistors, capacitors, inductors to provide some examples, integrated with or deposited on a substrate by a continuous series of compatible processes. The auxiliary devices may operate at voltages above a breakdown voltage of the transistors contained within the integrated circuit. As the operating voltages applied to the transistors increase, the transistors will eventually breakdown allowing an uncontrollable increase in current. Breakdown voltage is a voltage level where this uncontrollable increase in current occurs. Examples of breakdown may include punch-through, avalanche breakdown, and gate oxide breakdown to provide some examples. Operating above the breakdown voltage for a significant duration reduces the lifetime of the transistors.
Techniques are currently available to increase the voltage at which the breakdown occurs. These techniques may include separate design of input-output circuits using a high voltage process, double diffused drain or other extended drain techniques, or cascading of individual transistors to provide some examples. However, these techniques often increase the fabrication cost and/or complexity by requiring additional process steps along with additional substrate masking.
What is needed is a metal oxide semiconductor field effect transistor (MOSFET) device that addresses one or more of the aforementioned shortcomings of conventional MOSFET devices.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.